Impeller Replacement - Among other things

[mythx]

I'm going to remove the lower unit of my motor. It's a 1979 Mercury 50. I found this part number: 47-89983T MOD EDIT - Remove competitor. It seems to be the one for my unit. It seems there should be a kit to include gaskets and other items that should be replaced while I'm in there. If so, can someone point me to the right place? If not, what other items should I tackle while I have the lower unit off? Is there a specific gear oil I should use for it?

I don't know the history of this motor. I got it running last week, and it moved water. This morning, I fired it up, but it doesn't move water.

I wanted to change the fuel filter, but I'm not finding one. I can follow the fuel line all the way to the carbs. Is there an inline filter I should install?

Thanks in advance for the help.

 

[racerone]

There might be a screen / strainer on the fuel pump.----I normally use factory / quality impellers.

 

[mythx]

There might be a screen / strainer on the fuel pump.----I normally use factory / quality impellers.

Thanks for the reply. Guess I need to go hang out at my local boat shop

 

[JDusza]

I'm going to remove the lower unit of my motor. It's a 1979 Mercury 50. I found this part number: 47-89983T MOD EDIT - Remove competitor. It seems to be the one for my unit. It seems there should be a kit to include gaskets and other items that should be replaced while I'm in there. If so, can someone point me to the right place? If not, what other items should I tackle while I have the lower unit off? Is there a specific gear oil I should use for it?

I don't know the history of this motor. I got it running last week, and it moved water. This morning, I fired it up, but it doesn't move water.

I wanted to change the fuel filter, but I'm not finding one. I can follow the fuel line all the way to the carbs. Is there an inline filter I should install?

Thanks in advance for the help.

Couple things:
First, run a thin wire up the water telltale hole vigorously a few times. Sometimes insect eggs or small debris gets trapped and blocks water flow making you think the impeller is shot. Do this before you tear down the lower unit.
Second, if you're in the lower unit for the impeller I would also recommend replacing the adjacent water line rubber seal, 26.38452; item #27 on the exploded view parts list. Sometimes they get squished and start to break apart blocking the water line and for $4 extra it's worth the peace of mind.
Third, if there is no fuel filter between the connector and carburetor then the filter will either be a screen within the fuel pump or a screen within the carburetor. Depends on which 50 hp you have. To be certain, provide engine serial number. Is it a 3 or 4 cylinder engine?
Fourth, any good quality gear oil 80w90 will be acceptable. If the old oil that comes out is milky then it has been contaminated with water and there is a leaking seal which needs to be addressed.
J

 

[mythx]

Couple things:
First, run a thin wire up the water telltale hole vigorously a few times. Sometimes insect eggs or small debris gets trapped and blocks water flow making you think the impeller is shot. Do this before you tear down the lower unit.
Second, if you're in the lower unit for the impeller I would also recommend replacing the adjacent water line rubber seal, 26.38452; item #27 on the exploded view parts list. Sometimes they get squished and start to break apart blocking the water line and for $4 extra it's worth the peace of mind.
Third, if there is no fuel filter between the connector and carburetor then the filter will either be a screen within the fuel pump or a screen within the carburetor. Depends on which 50 hp you have. To be certain, provide engine serial number. Is it a 3 or 4 cylinder engine?
Fourth, any good quality gear oil 80w90 will be acceptable. If the old oil that comes out is milky then it has been contaminated with water and there is a leaking seal which needs to be addressed.
J

Thank you J, that is very helpful, and exactly what I was asking for. I did stick a wire up the telltale, and actually removed the hose from the engine and was able to blow through it. The other day when I started it, water came out immediately. When I didn't get that result today, I only allowed the motor to run for about 60 seconds. Is there a thermostat that should open first, or should water start flowing right away?

There is a lot of grease on the front side of the lower unit, and I've noticed a couple spots on my driveway. Does that point to anything specific I should look at?

Thanks again, I really appreciate the response.

It's a 4 cylinder BTW - 5337699

 

[racerone]

Water should come out of the tell tale within seconds of the motor starting !----No thermostat on those models.

 

[JDusza]

1 For this model it looks like the fuel filter screens are within the fuel pumps attached to the carburetors.
2 Not sure about the grease on the lower unit. Clean it all off with some old gas and watch for new leak tell tales. Might be a sign that that the lower unit is leaking but that's gear oil and shouldn't be greasy. Tough to say. Once clean, keep an eye on the fill hole for a leak.
Another couple parts you want to change at maintenance are the washers used on the lower unit fill and vent holes. They get crushed and malformed with use and should be replaced at oil changes. Item #32 on exploded parts list view, part number 12.19183.3, washer.
3 In my lower unit gear boxes and 4.stroke sumps I use an ounce of MotorKote to guard against friction from oil contamination or seal failure . Not sure if anyone else is a believer in this product.
J

 

[JDusza]

Another thought.
In going after the impeller you may also want to order a replacement drive key in the even you drop or lose the lose the original. Item 23 on parts list exploded view, 28.8M0032837, Key. Again, $4 peace of mind.
J

 

[racerone]

I do not believe these motors left the factory with an overheat warning or shutdown system.----It would run till it destroyed itself.------A wise man would install a new factory impeller every 3 seasons !!--A " new to you motor " must have a new impeller installed.

 

[mythx]

I love the $4 peace of mind ideas.

Thank you very much.

I'll get it cleaned up and pay attention to it.

Thanks again

 

[mythx]

Update.

I replaced the impeller, but still no pee. I was careful to ensure the impeller pointed the same direction as the one I removed.

I know it's clear between the engine and the telltail. I was sure to get the water tube to align properly with the water pump. That was something I double checked.

What's my next troubleshooting step? I'm thinking I should have stuck the lower unit in a bucket of water and figured out a way to spin the drive to rule out the rest of the lower unit.

Thanks again for the help.

 

[racerone]

Those pumps are very simple.---- Hard to assemble it so that it will not work.----Put boat in water for a proper test.

 

[mythx]

Those pumps are very simple.---- Hard to assemble it so that it will not work.----Put boat in water for a proper test.

Thanks. I used a garden hose and ear muffs. Is that not a sufficient test?

 

[mythx]

Hi, just wanted to followup. I pulled the lower unit off again. Didn't find the issue, but used some compressed air to confirm there is no blockage. I reassembled everything and now it's peeing as it should. Not sure if I did something wrong initially, or dislodged something with the compressed air, but it's working now.

Thanks for your help. Now to move on to carb tuning.